Transfer ribonucleic acid (tRNA) molecules are indispensible parts of the protein synthesizing machinery of all living cells because they supply the proper amino acid for the translation of messenger RNA. However, tRNA molecules also participate in regulatory roles in both transcription and translation thereby affecting the activity of genes. It has been postulated, therfore, that alterations in tRNAs control certain aspects of cellular development. It is the objective of this proposal to investigate molecular alterations in tRNAs which occur during normal cell differentiation and neoplastic development. Our approach will be to identify the kinds of alterations in tRNAs which occur under conditions of cellular development, to characterize the structural nature of the alterations, and to identify the nature of any change in biological function of the altered tRNA. Our methods involve column chromatography of tRNA species on reversed-phase and Aminex A-28 columns for fractionation and purification of tRNA species, structural studies on primary sequence and degree of modification using reversed-phase columns for the separation of oligonucleotides and Aminex A-6 as well as two dimensional, thin-layer chromatography for the separation and identification of nucleosides, and functional studies on codon response, availability for translation, and repression of biosynthetic enzymes. Because of our experience with bacterial cells, we have chosen to investigate alterations in tRNAs which occur during bacterial sporulation as a model system.